Getting a Handle on Legacy Code

We all run into legacy code. Sometimes, we even write it ourselves. Working with legacy code can be a daunting challenge, but there are ways to tackle it without taking on the risk of a full rewrite.

There is a deep satisfaction that comes from conquering a nasty piece of legacy code. The ability to achieve this goal depends on both testing and refactoring.

We'll learn how baby-step refactoring techniques lead to a better understanding of the code and a high-quality design while always keeping the code running.

This is a workshop, so a lot of the material was hands-on practice and not captured in these slides.

Transcript

1. www .codingzeal.com @codingzeal Randy Coulman Getting a Handle on Legacy Code Senior Software Engineer @randycoulman
2. Welcome to our new job! Enhance the inventory management system for the Gilded Rose Inn
3. The System
4. The System • Items have a sell_in value: the number of days we have to sell the item
5. The System • Items have a sell_in value: the number of days we have to sell the item • Items have a quality value: how valuable the item is
6. The System • Items have a sell_in value: the number of days we have to sell the item • Items have a quality value: how valuable the item is • At the end of each day our system lowers both values for every item
7. The Spec: Can We Trust It? • Once the sell-by date has passed, quality degrades twice as fast • The quality of an item is never negative • “Aged Brie" actually increases in quality the older it gets • The quality of an item is never more than 50 • "Sulfuras", being a legendary item, never has to be sold or decreases in quality • "Backstage passes", like aged brie, increases in quality as its sell-by date approaches; quality increases by 2 when there are 10 days or less and by 3 when there are 5 days or less, but quality drops to 0 after the concert.
8. Constraint The Item class and @items property are off-limits No collective code ownership
9. Our Task: Support Conjured items Conjured items degrade in quality twice as fast as normal items
10. Workshop Structure Mix of: • Presentation/demo • Mob programming • Small group/pair/individual work
11. Mob Programming • One computer for programming • One driver • N navigators and researchers http://mobprogramming.org/mob-programming-basics/
12. Legacy Code How do we safely change legacy code?
13. The Legacy Code Algorithm
14. The Legacy Code Algorithm 1. Identify change points
15. The Legacy Code Algorithm 1. Identify change points 2. Find test points
16. The Legacy Code Algorithm 1. Identify change points 2. Find test points 3. Break dependencies
17. The Legacy Code Algorithm 1. Identify change points 2. Find test points 3. Break dependencies 4. Write tests
18. The Legacy Code Algorithm 1. Identify change points 2. Find test points 3. Break dependencies 4. Write tests 5. Make changes and refactor
19. The Legacy Code Algorithm https://twitter.com/mfeathers/status/589118880825495552
20. Code For the Workshop https://github.com/CodingZeal/gilded-rose-railsconf2015
21. The Code
22. Mob Programming Exercise Write characterization tests
23. Golden Master Testing a.k.a. Guru Checks Output anti-pattern Katrina Owen’s Approvals Gem
24. Mob Programming Exercise Use Approvals to simplify testing
25. Cleaning Up the Code Fight the urge to rewrite
26. Cleaning Up the Code The Boy Scout Rule: "Leave the campground cleaner than you found it"
27. Cleaning Up the Code Baby Steps Lots of tiny, safe refactorings add up to big changes
28. Cleaning Up the Code Don’t Boil the Ocean Stay focused
29. Cleaning Up the Code https://twitter.com/KentBeck/status/250733358307500032
30. Cleaning Up the Code https://twitter.com/supermoof/status/478322429257715712
31. Mob Programming Exercise Refactor for better test points
32. Small Group Exercise Write a few more-targeted tests
33. Small Group Exercise Refactor enough to add new feature
34. Mob Programming Exercise More refactoring
35. Public Service Announcement
36. Want More? Original Gilded Rose Kata http://craftsmanship.sv.cmu.edu/katas/gilded-rose-kata Gilding the Rose Talk at GoGaRuCo 2014 http://confreaks.tv/videos/gogaruco2014-gilding-the-rose-refactoring-legacy-code Code from GoGaRuCo 2014 Talk https://github.com/randycoulman/GildedRose
37. References Working Effectively With Legacy Code: Michael Feathers http://www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/dp/0131177052 Refactoring: Martin Fowler http://www.amazon.com/Refactoring-Improving-Design-Existing-Code/dp/0201485672
38. References Approvals https://github.com/kytrinyx/approvals SimpleCov https://github.com/colszowka/simplecov Flog https://github.com/seattlerb/flog
39. Questions ? http://randycoulman.com http://speakerdeck.com/randycoulman http://speakerrate.com/randycoulman Code is on Github https://github.com/CodingZeal/gilded-rose-railsconf2015
40. www .codingzeal.com @codingzeal Thank You! Randy Coulman @randycoulman